Since July of 1997, 11 child study participants have been re-evaluated at CHOP. No new child subjects have been enrolled. The investigators expect to enroll one new child subject during the coming year. One child study participant experienced an untoward event during her routine evaluation. On August 12, 1998 an 11 year old female study participant underwent a cardiac catheterization at CHOP. Her left internal mammary artery dissected during the procedure and subsequently she had a coronary artery bypass graft perfomed that evening. She has recovered well. This participant is not one of the five participants who received ex vivo gene therapy. The study team has initiated a lipoprotein kinetic study for the adult subjects at HUP. Participation in this study is optional and is conducted concurrently with the annual routine evaluation. Several adults have participated and the preliminary data are currently being evaluated by the investigators.